Method of making molds



June 14, 1938. H. ASSBROICHER ET AL, 2,120,881

. METHOD OF MAKING Moms Filed Nov. 25, 1936 2 Sheets-Shee t 1 mvzn-rozs HEINZ ASSBROICHER AND KARL HUFF- by Meir afiarweys June 14, 1938. H. ASSBRO ICHER'ET AL I 2,120,881

' METHOD OF MAKING MOLDS Filed Nov. 25, 1936 2 Sheets-S heet 2 INVENTORS HE|NZ ASSBROICHER AND KARL HUFF Patented June 14, 1938 UNITED STATES- METHOD OF MAKING MOLDS Heinz Assbroicher, Hanover-Kleefeld, and mm Huff,

Hanover-Herrenhausen, Germany, as-

- signors to Continental Gummi-Werke Aktiengesellschaft, Hanover, Germany Application November 25, 1936, Serial No. 112,800

In Germany November 28, 1935 3 Claims.

Vulcanizing molds of cast steel and cast iron circular convex and a semicircular concave cross for use-in making the tire outer covers and inner tubes and like articles are already known, but as these molds are very liable to fracture, it is necessary for their walls to be made'comparatively thick, so as to enable them to withstand the pressures set up in the course of vulcaniza-.

tion. Such molds are, therefore, uneconomical, both as regards cost of material and in actual 1o handling means have to be provided'fortransporting these heavy molds and, what is more, they require the use of boiler presses or autoclaves; the thick wall of the molds .has to be heated up for eachvulcanization and, consequently, the complete heating process is rendered both costly and' tedious.

It is also known to make hollow annular tire molds from sheet metal, pressed out between'a matrix and a; die, to correspond to the profile of the tire, such molds consisting of two parts mutually abutting on the lines of greatest and smallest circumference of the hollow ring. The production of these separate parts, from sheet metal is, however, very costly because it requires the use of such powerful (and, therefore, ex,- pensive) dies and because such enormous pressures have to be developed by the die presses.

For this reason, alone, the use of these pressed sheet metal molds is absolutely precluded in the case of tire manufacturers who are turning out a large number of different types and patterns of tires. In addition to this, the methods of manufacture hitherto used for the production of sheet metal molds have been found vto'involve diifi- I 5 culties in connection with the formation of the profile or tread pattern matrix in the mold.

These difllculties have only been overcome by further subdividing the two halves of the hollow ring, which expedient, however, necessitates the 40 use of complicated devices for'holdin'g the several parts together. This way oi making tire molds has not come into extended use because of the need for providing a heavy and costly die outfit -inrespect of each and every type and size of tire to be produced.

It isan object of the present invention to provide a method of making sheet metal molds which is cheap, owing to the simplicity of the tools required and a further'object is to enable the profiles .tobe produced easily, without being compelled to'sacrifice the unity of each half of themold.

Thei first of these objects is achieved by shap- ,ing up 'two pieces oftube, by means of calibre re -rolls, into two rings, having, respectively a semi- 'section, the hollows of said cross sections opening in opposed radial directions so that the twosemicircular rings, when brought-together, form-a hollow ring of circular cross section. The advantage of this method is that tire molds of various difierent diameters can be produced with one pair of rolls, since the size is not dependent on the tools but is determined, in each case, by the development stretching of the material of the 10 ring to be shaped. Each of the two rings thus produced (i. e. the outer and the inner ring), is then cut in two along the line of its greatest and or its smallest circumference, as the case drawings, in which V Figure 1 shows one piece of tube as it appears prior to being shaped in to a concave ring, as, 30 shown in Figure 2.

Figures 3 and 4 show, respectively, a second. piece of tube and itsformation into a convex ring. t

Figure 5 shows how the concave and convex rings of Figures 2 and 4, being complementary to each other, form togetheryahollow ring of circular cross section.

It will be observed that these rings abut along 40 4 the lines of the mean circumference. Thus in the outer and convex ring the profile ortread pattern can be formed directly, and without hindrance, by embossing or milling.

Figure 6 shows an outer ring so treated, drawn a .to a larger scale.

Figure 7 shows the inner ring, likewise drawn to a larger scale than the preceding figures.

These two rings are now divided in medial, planes indicatedby line :r- -zc in Figure 6 and by 50 line y-y in Figure '7, the actual lines of separation being at the greatest and at the smallest circumference, respectively, so that four rings a, b,- c, d of quadrantal cross section, are formed, as indicated in I 5 Figure 8 diagrammatically (drawn to the same scale as Figures 1 to The rings a, c on the one hand, and the rings b, d on the other hand, are now united at the lines e corresponding to the mean circumference, as shown in Figure 9, which like Figure 10, is drawn to the same scale as Figures 6 and '7. The dotted line zz in Figure shows the line of division of the finished mold, the halves of which are each in one piece, since the homogeneous union of. the material is en-, sured by welding. v

Figures 11 and 12 are front and side elevations,

' respectively of the calender.

A mold produced in this way is cheap to construct and, in use, it responds perfectly to all I practical requirements.

Whereas the weight of the cast molds, hitherto used, amounted say, to about 400 to 450 kilograms, the new mold weighs only about 60 to 75 kilograms, while additional fittings; such as are required with the previously known sheet metal molds and which, again increase the weight, are not necessary.

The calender used for shaping the pieces of tube shown in Figures 1 to 4 is shown in front and side elevation respectively, in Figures 11 and 12.

The two standards I and 2 include guideways for slides 3 and 4 in which is mounted the upper shaft 5 carrying, near its free or overhanging end, the 'convex profiling roll 6. Below the shaft 5, in the standards I and 2 is mounted the lower shaft 1, which carries on one end, a driving The annular blank or piece of tube l6, which,

is to be shaped is hung on the lower profiling roll 9 and the upper shaft, with the upper profiling roll 6 is then forced downwardly towards the said lower roll, so that when the shaft 1 is rotated the annular blank I6 is rotated also and shaped at the same time. A ring with a concaved periphery (corresponding to the periphery of the lower roll 9) results.

If the two profiling rolls be now interchanged the lower roll 9 being shifted to the top shaft 5 and the upper roll 6 to the bottom shaft I, the press-rolling of an annular blank such as III will yield a ring with a convex periphery.

The calibration or profiling of the rolls is such as to compensate for the width of cut when the convex and concave rings are respectively divided.

We claim:

'1. A process for the manufacture of thinwalled, hollow annular sheet metal molds, for use in the vulcanization of tires and the like and consisting of two parts abutting along the lines of the greatest and smallest circumferences of .the hollow ring, which comprises shaping two pieces of tube by calibre rolls into two rings of semicircular, convex and concave radially opening cross section, which, together, form a hollow ring, then cutting the said convex and concave rings along the lines of the greatest and the smallest circumference, respectively, thereafter pairing the resulting outer and inner rings and then uniting each pair, consisting of an outer and an inner ring, by welding along the line of mean circumference.

2. Process according to claim 1, characterized by,forming the tire profile or tread pattern in the outer convex rings, as for instance by an embossing or milling action prior to welding the said outer rings to the inner rings.

3. Process according-to claim 1, characterized by forming the tire profile or tread pattern in the outer convex. ring, as for instance, by an embossing or milling operation before cutting the said outer ring in two.

HEINZ ASSBROICHER. KARL HUFF. 

